September 9th, 2020

лошадь, диаграмма, Фейнман

О происхождении гигантского дипольного резонанса

Эх, не было у меня такого текста на 4 курсе!...

The Origin of the Giant Dipole Resonance
Richard B. Firestone
The Giant Dipole Resonance (GDR), which is conventionally described as due to collective motion, is instead shown to be the result of a sudden increase in level density at the 2h{\omega} shell closure. The energy of the GDR closely follows the shell model harmonic oscillator energy model where h{\omega} = 39A^-1/3, for heavy nuclei. A better fit covering the entire mass range is given by h{\omega} = 47:55(0:13)(A^-1/3 - A^-2/3). The GDR is shown to be composed of a lower energy peak, E1, corresponding to the population of levels with oblate deformation and a higher energy peak, E2 corresponding to the population of levels with prolate deformation. The peak energy separation is proportional to the \beta_2 deformation and given by E2-E1 = 11:03(0:22)|\beta_2|. The total photonuclear cross section, sigma = sigma1 + sigma2, populating the GDR is proportional to the level density at the GDR and is given by sigma = 0:483(0:006)A^4/3 where sigma1 = sigma2. The widths of the two GDR peaks are consistent with Nilsson model predictions and found to be Gamma1 = 7:41(0:15)A^-1/6 MeV and Gamma2 = 11:13(0:16)A^-1/6 respectively. The Standard Lorentzian model parameters are fitt to high accuracy as a function of mass and deformation and can be applied reliably to all nuclei. It is shown that the energies of pygmy and spin flip resonances correspond to the E = h{\omega} harmonic oscillator energy and that the giant quadrupole (GQR), giant monopole (GMR), and giant octupole (GOR) resonances coincide with the E = 2-4 h{\omega} harmonic oscillator energies where the level density suddenly increases at the shell gaps.
Comments: 7 pages, 6 figures
лошадь, диаграмма, Фейнман

Об обсчете излучения Смита-Парселла

Frequency-domain calculation of Smith-Purcell radiation for metallic and dielectric gratings
Andrzej Szczepkowicz (1), Levi Schachter (2), Joel England (3) ((1) University of Wroclaw, (2) Technion, (3) SLAC)
The intensity of Smith-Purcell radiation from metallic and dielectric gratings (silicon, silica) is compared in a frequency-domain simulation. The numerical model is discussed and verified with the Frank-Tamm formula for Cherenkov radiation. For 30 keV electrons, rectangular dielectric gratings are less efficient than their metallic counterpart, by an order of magnitude for silicon, and two orders of magnitude for silica. For all gratings studied, radiation intensity oscillates with grating tooth height due to electromagnetic resonances in the grating. 3D and 2D numerical models are compared.
Comments: 19 pages, 7 figures, 4 tables
лошадь, диаграмма, Фейнман

К двадцатилетию расщепления фотона

Статья Зураба Силагадзе на русском. Подробно вспоминает о Дельбрюке, но ни слова о работе Ландау, Ахиезера и Померанчука!


Photon splitting -- twenty years later
Z.K. Silagadze
In 1995, a team of physicists from the Budker Institute of Nuclear Physics in Novosibirsk was able to observe the splitting of a photon in the Coulomb field of an atomic nucleus for the first time, and reported the preliminary results of this experiment at two conferences. This was an extremely difficult experiment as the probability of the process is very small. It took another seven years to publish the final results. This story has been further developed recently. The ATLAS detector at the Large Hadron Collider observed in ultra-peripheral heavy ion collisions a process related to the photon splitting - light by light scattering. In addition, a team of Italian, Polish and British astrophysicists obtained the first observational evidence of the existence of vacuum birefringence in the magnetic field of an isolated neutron star - another physical phenomenon also related to the photon splitting. These new developments triggered this essay, written several years ago.
Comments: 10 pages, in Russian